The invention applies in particular, but in non-limiting manner, to large installations, e.g. 250 MW to 600 MW, that include a plurality of cyclone separators placed side by side at the outlet from the furnace. In such installations, there is a lack of room for positioning the inlet ducts to the separators properly because of the space occupied to pass various beams. Thus, conventionally, the disposition of the inlet duct to a cyclone separator at the outlet from a furnace is as shown in FIG. 1, which is a diagrammatic plan view of a cyclone separator 1 together with its inlet duct 2 at the outlet from the furnace 3. This inlet duct has two side faces 4 and 5, together with a bottom face and a top face that are not visible in this view.
The face 4 is referred to as the "intrados" face and terminates at the tip of the cyclone D, while the face 5 is referred to as the "extrados" face.
Having the duct positioned in this way, due as mentioned above to lack of space, is not favorable to obtaining a separator that works with good efficiency.
Given that the duct is very short, solids present in the top portion thereof do not have time to settle out within the duct. As a result, a large fraction of these solids reach the inlet to the cyclone via the top portion of the duct, from which a non-negligible proportion of them is entrained into the gas outlet from the cyclone.